AGEIOCHOERUS. 27 



The inner lobes are smaller than those external, are convex internally, and con- 

 cave externally with a slight median elevation. The extremities of the summits 

 extend around the base internally of the outer lobes, except that posterior of the 

 antero-internal lobe, vrhich ceases abruptly at its arrival in the transverse valley 

 of the tooth. 



Constituent portions of a basal ridge, feebly developed, exist principally between 

 the bases of the inner lobes, and anteriorly and posteriorly. 



The fourth premolar is quite peculiar, and rather resembles a last deciduous 

 molar than the permanent premolars of ordinary ruminants. It consists of two 

 pairs of lobes like those of the true molars, but the postero-internal lobe is in a 

 rudimentary condition, consisting of a small pyramidal tubercle occupying the 

 normal position. The prominence externally produced by the confluence of the 

 outer lobes is relatively not so large as in the true molars, but otherwise the prin- 

 cipal lobes have the same form. 



The third premolar consists of one large trihedral pointed lobe, with a rela- 

 tively small pyramidal lobe, situated at the base of its postero-internal face. The 

 latter lobe is broken, in the specimen. The external face of the former is the 

 broadest, is slightly convex, and is prominent in the median line. The inner faces 

 are sloping, and that posteriorly is concave. 



The second premolar has nearly the same form as that last described. Its prin- 

 cipal lobe is relatively less broad, and its external face is more convex. A rudi- 

 mentary lobe, which apparently existed at the base of the postero-internal face of 

 the principal lobe, is broken away in the specimen. 



The upper true molars are implanted by four fangs; the last premolar by three; 

 and those in advance by two. The fangs of the anterior premolars, and the outer 

 ones of the last premolar and the true molars, present a remarkable curve outward 

 in their course downward. 



Inferior molars. — (Figs. 7-9.) The outer lobes of the lower true molars are larger 

 than those within, but do not rise quite so high. Their internal face is concave and 

 slightly elevated in the median line. Externally they are conoidal, are confluent 

 at the base, are without intervening portions of a basal ridge, and are slightly 

 spread outwardly towards their lateral margins. 



The anterior extremity of the summit of the antero-external lobe joins the con- 

 tiguous margin of the lobe within ; its posterior extremity in association with that 

 anterior of the summit of the postero-external lobe turns upward and becomes con- 

 fluent with the posterior part of the external face of the antero-internal lobe; and 

 the posterior extremity of the postero-external lobe, except that of the last molar, 

 bifurcates, one portion connecting itself with the posterior part of the outer face of 

 the postero-internal lobe, the other with the posterior margin of the same lobe. 



The inner lobes externally are convex and nearly vertical, and internally are 

 most prominent in the median line, and have their angles everted into short, promi- 

 ent, divergent folds. 



The fifth lobe of the last molar is about the size of those external, and in section 

 is oval. Its pointed summit descends by a pair of U like arms, one of which joins 



